The process with present invention relates to downhole drilling in shales/coal seams. More particularly, the present invention relates to a process to increase the area of microbial stimulation in a methane gas recovery area in a multi seam coal bed/methane dewatering and depressurizing production system through the use of horizontal or multilateral wells in place of a plurality of vertical wells.
2. General Background of the Invention
It is being increasingly recognized in the industry in recent years that methane production can be obtained within shallow to very deep coal or shale beds within the earth's strata. Such an observation was deduced from studies of coal gases, changes in coal gas chemistry, and the bio-degraded nalcane pattern of some coal extract samples. In fact, the inventor in this application has developed a process utilizing underbalanced drilling into multiple coal and shale formations and dewatering the drill formations, which includes a process so that a lateral or horizontal borehole can be drilled within the coal seam, through a process which is covered in U.S. Pat. No. 6,923,275 and its related U.S. Pat. No. 6,457,540. In the patented process, the methane gas can be collected from multiple coal seams through the gas collection annulus and the water when collected where the methane gas is entrained, can be returned downhole for disposal and/or isolation.
What has become well known in the art, is that one can undertake a process for stimulating microbial activity in hydrocarbon-bearing subterranean formations. Such a process is found, for example, in U.S. Pat. No. 6,543,535 (the '535 patent) for stimulating the activity of microbial consortia in a subterranean formation to convert hydrocarbons to methane, which then can be produced, said patent which in its entirety is incorporated herein by reference thereto. One of such microorganism disclosed in the '535 patent is a methanogenic microorganism for example. The presence of microbial consortia is determined and a characterization made of at least one microorganism of the consortia, being a methanogenic microorganism. Therefore, by stimulating the coal/shale bed, the methane gas can be produced more readily, and it is then returned to the surface for collection in at least one of the processes as discussed above.
Currently, in the art of injecting microbes to stimulate a coal formation, of which applicant is aware, the only type of delivery system which is undertaken in the art, would be to drill a vertical well down into the formation, for example, as found in U.S. Pat. No. 6,817,411 and as discussed and found in U.S. Pat. No. 5,669,444. In the reading of the current state of the art, the vertical well is drilled to a depth within the coal seam, and at that point, the coal bed is stimulated with a consortia of microorganisms pumped into the formation and allowed to react with the coal/shale bed, and in turn enhance the production of methane within the confined area around where the vertical well is drilled. One of the short-comings in this particular current state of the art, is that usually a coal bed, although not necessarily thick, is spread over a wide area, and therefore, if one were to attempt to stimulate all of the coal bed through the use of a vertical well, it is foreseen that there would be a need for numerous vertical wells to be drilled into the subterranean coal formation in order to maximize the stimulation of the coal formation cleats. One can only surmise that the drilling of numerous vertical wells or directional wells from numerous well location pads, would be an extremely expensive and time-consuming undertaking and would not necessarily be a viable method of achieving maximum areal contact and sweep within the coal formation, in addition due to low injection pressures as to not exceed the fracture gradient in vertical wells it would be impossible to maintain constant reservoir pressure via inter-well bore connectivity. Therefore there is a need in the industry for a process which would enable one to enter the subterranean formation with non fluid invasive and contaminating drilling and completion techniques. A process to stimulate a vast area of the subterranean coal seams with a large areal contact with the cleat system of the coal formation. This can be performed at low injection pressures while maintaining an ecological environment that promotes the in-situ microbial degradation of hydrocarbons to methane gas.